Mechanistic studies of the radical SAM enzyme spore photoproduct lyase (SPL).
Mechanistic studies of the radical SAM enzyme spore photoproduct lyase (SPL).
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DOI：
10.1016/j.bbapap.2011.11.008
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发表时间：
2012-11
影响因子：
3.2
通讯作者：
Li, Lei
中科院分区：
文献类型：
--
作者：
Li, Lei
孢子光产物裂解酶（SPL）在细菌萌发早期修复一种特殊的胸腺嘧啶二聚体5-胸腺嘧啶-5，6-二氢胸腺嘧啶，通常称为孢子光产物或SP。SP是细菌内生孢子中唯一的DNA光损伤产物，它的产生和SPL的快速修复是孢子极高抗紫外线的原因。早期的体内研究表明，SPL利用直接逆转策略在缺乏光的情况下修复SP。在过去的十年中的研究进一步确定SPL作为一种自由基SAM酶，其利用三半胱氨酸CXXXCXXC基序来携带[4Fe-4S]簇。在1+氧化态下，簇为S-腺苷甲硫氨酸（SAM）提供一个电子，SAM作为第四和第五配体以双齿方式与簇结合，以还原性切割SAM中与锍离子相关的C-S键，产生反应性5′-脱氧腺苷（5′-dA）自由基。这个5′-dA自由基从SP的C6碳原子上夺取proR氢原子以启动修复过程;所产生的SP自由基随后断裂以产生推定的胸腺嘧啶甲基自由基，其接受反馈的H原子以产生修复的TpT。SAM建议在每个催化循环结束时再生;并且在SPL反应中仅需要催化量的SAM。用于回授步骤的H原子源建议为半胱氨酸残基（B中的C141）。subtilis SPL），并且H-原子转移反应在蛋白质上留下硫酰基自由基。因此，这个硫酰基自由基一定参与了SAM的再生过程;然而，硫酰基自由基如何从5′-dA上夺取一个H原子来再生SAM尚不清楚。本文回顾和讨论了声压级机理解释的历史和最新进展。尽管最近取得了一些突破，但在对这种有趣的DNA修复酶的机械理解方面提出了更多的问题。
Spore photoproduct lyase (SPL) repairs a special thymine dimer 5-thyminyl-5,6-dihydrothymine, which is commonly called spore photoproduct or SP at the bacterial early germination phase. SP is the exclusive DNA photo-damage product in bacterial endospores; its generation and swift repair by SPL are responsible for the spores’ extremely high UV resistance. The early in vivo studies suggested that SPL utilizes a direct reversal strategy to repair the SP in the absence of light. The research in the past decade further established SPL as a radical SAM enzyme, which utilizes a tri-cysteine CXXXCXXC motif to harbor a [4Fe-4S] cluster. At the 1+ oxidation state, the cluster provides an electron to the S-adenosylmethionine (SAM), which binds to the cluster in a bidentate manner as the fourth and fifth ligands, to reductively cleave the C-S bond associated with the sulfonium ion in SAM, generating a reactive 5′-deoxyadenosyl (5′-dA) radical. This 5′-dA radical abstracts the proR hydrogen atom from the C6 carbon of SP to initiate the repair process; the resulting SP radical subsequently fragments to generate a putative thymine methyl radical, which accepts a back-donated H atom to yield the repaired TpT. SAM is suggested to be regenerated at the end of each catalytic cycle; and only a catalytic amount of SAM is needed in the SPL reaction. The H atom source for the back donation step is suggested to be a cysteine residue (C141 in B. subtilis SPL), and the H-atom transfer reaction leaves a thiyl radical behind on the protein. This thiyl radical thus must participate in the SAM regeneration process; however how the thiyl radical abstracts an H atom from the 5′-dA to regenerate SAM is unknown. This paper reviews and discusses the history and the latest progress in the mechanistic elucidation of SPL. Despite some recent breakthroughs, more questions are raised in the mechanistic understanding of this intriguing DNA repair enzyme.
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